1. Field of the Invention
The invention relates generally to electromagnetic imaging, and more particularly to imaging techniques that operate in the terahertz frequency range.
2. Background Art
Time-domain measurements of electromagnetic radiation in the terahertz frequency range have been used in the operational environment of spectroscopy. However, the use of terahertz electromagnetic radiation to provide an image of an object in real time is impractical due to the relatively long acquisition time required for terahertz waveforms. This acquisition time is typically in the range of minutes. Using pulses of terahertz radiation, one presently-existing terahertz ("T-ray") imaging technique reduces the acquisition time of a single terahertz waveform from several minutes to several milliseconds, while still maintaining a reasonable signal-to-noise ratio. Examples of this technique are disclosed in U.S. Pat. No. 5,623,145 issued Apr. 22, 1997, to Martin C. Nuss and also in patent application Ser. No. 08/711,146, filed Sept. 9, 1996, M. C. Nuss now U.S. Pat. No. 5,789,750. However, this technique does not explicitly utilize the time-domain nature of the terahertz waveform. Consequently, the displayed images only show the transmitted or reflected power, obtained by integrating the Fourier spectrum of the terahertz waveform with a digital signal processor (DSP). Such an image is not a full-volume image, which is defined as an image that shows the locations of compositional discontinuities within the volume of an object. Images that only show transmitted and/or reflected power do not reveal compositional information about an object including the locations of discontinuities. What is needed is an improved terahertz imaging technique which provides depth resolution and compositional information about an object in real time.